The present invention relates to a pneumatic radial tire having block patterns and more particularly to the pneumatic radial tire which makes it possible to improve wear resistance without affecting driving performance virtually.
In general, with the pneumatic radial tire, center wear and uneven wear are occurred on a tread, and it is a determined to be wear life when at least a portion of those wear is reached the minimum-required groove depth. Accordingly, various methods for prolonging the wear life by changing tread extension width and groove area have been proposed.
However, there have been problems that extending the tread extension width leads to increases in weight and cost, as well as the tire becomes tendency to be trapped by a rut, as a result, the so called rut-wandering property is deteriorated, on the other hand, reducing groove area decreases a traction performance and a driving performance on a wetted road surface, for example. Moreover, there has been a disadvantage that, although wear resistance can be improved in the case of constituting directional tread patterns which a tire rotation direction is specified, constraints on use of the tire are increased.
The object of the invention is to provide a pneumatic radial tire which makes it possible to improve wear resistance without affecting a driving performance virtually.
The pneumatic radial tire according to the invention for accomplishing the object described above, comprises a constitution wherein five main grooves extending in the circumferential direction of a tire are provided on a tread to divide into and form land portions of six rows, each land portion is divided into block rows constituted by a plurality of blocks by means of a plurality of subgrooves extending in the direction of width of the tire so as to define a first block at each shoulder side, a second block row at each shoulder side and a block row at a center side, and an area ratio of the blocks is set at a relationship of 1:0.9 to 1.1:1.8 to 2.2 of the blocks of the first block row at the shoulder side to the blocks of the second block row at the shoulder side to the blocks of the block row at the center side, in a region between ends of a belt layer having a maximum width embedded in said tread.
As described above, even though the tire performance such as the traction performance can be reserved by increasing the ratio of the groove area by setting the area ratio of the blocks at the relationship of 1:1:2 (the variation within the range of xc2x110% will be permitted) from the block row of the shoulder side to the block row of the center side, the wear resistance can be improved.
According to the invention, the area of each block, the total area of the tread and the groove area of the tread or the like have been measured in the region between the ends of the belt layer having the maximum width in the belt layer embedded in said tread. This region between the ends of the belt layer having the maximum width is substantially matched to a ground region where using the tire.
According to the invention, each land portion is divided into a plurality of blocks mainly using a plurality of subgrooves, which these plurality of subgrooves may be used with siping which are a direct extension thereof at the same time. Thus, the siping which are a direct extension of the subgroove behave with the subgroove, the siping contribute to dividing the blocks adjoining each other. Moreover, the siping which is not on an extension line of the groove, for example, the siping intersecting the groove and the siping being independently without communicating with the groove, may be provided as required in the blocks. Since an interval of such siping is not only narrow, but also behaves independently from the groove, the siping has no action capable of dividing the blocks into the further small blocks. Moreover, a groove which is narrower than the subgroove and is not more than 2.0 mm in width is referred to as a sipe.